Revert "Move metadata validation to CI build step"

This reverts commit ae02b138.

.gitlab-ci.yml

@@ -33,7 +33,6 @@ build wheel:
     # TODO:  consider moving git installation to ska-python-buildenv Dockerfile
     - apt-get -y update
     - apt-get install -y git --no-install-recommends
-    - scripts/validate-metadata.sh
     - python setup.py sdist bdist_wheel
   artifacts:
     paths:
@@ -89,6 +88,8 @@ publish to nexus:
     TWINE_USERNAME: $TWINE_USERNAME
     TWINE_PASSWORD: $TWINE_PASSWORD
   script:
+    # Check metadata requirements
+    - scripts/validate-metadata.sh
     - pip install twine
     - twine upload --repository-url $PYPI_REPOSITORY_URL dist/*
   only: